1. Field
The present invention relates to urgent deceleration indicating devices and systems and, more particularly to devices and systems that augment existing vehicle braking indicating devices and systems.
2. Related Art
Vehicles have long incorporated brake lights for warning others that the vehicle is decelerating. The brake lights are turned on when the brake pedal is depressed to indicate to the following driver that the vehicle is likely decelerating. However, the brake light merely indicates to the following driver whether the brakes are applied and give no indication as to the urgency of the braking condition or any indication of the magnitude of deceleration of the vehicle. Thus, the following driver must always be alert and realize that any illumination of a vehicle's brake lights can be a gentle deceleration or a sudden urgent deceleration.
Prior devices and systems have been described that detect and indicate the urgency of a braking condition by illumination of a light. Some of these warning devices are self-contained and include some means for detecting deceleration in the primary direction of vehicle motion. For example, these devices use one or more accelerometers to determine vehicle deceleration in the primary direction of vehicle motion. An indication, such as illumination of the light when the deceleration exceeds a threshold, is then provided.
Because these devices only detect acceleration and only in one direction, they do not measure acceleration independent of gravitational effects and, thus, are prone to false triggers or trigger failures if the vehicle is not in a horizontal orientation when it urgently decelerates. When the vehicle is tilted, e.g., on a slope, the acceleration due to gravity is sensed by the accelerometer, but is assumed to be driver induced by the control circuit of the device. Thus, because of the sensed acceleration due to gravity, these warning devices will cause a false trigger or will fail to trigger such as when the vehicle is travelling up or down a slope.
The prior art also shows that some false triggers or trigger failures may be decreased by warning systems that are responsive to other vehicle operating parameters such as pressure sensed in the hydraulic braking system, wheel velocity or slip sensed by the anti-lock braking system, or distance sensed by a proximity radar system. However, these warning systems are not self-contained, and in addition, require a complex system of multiple sensors with extensive wiring. As a result, these warning systems are difficult and costly to manufacture and install, particularly if retro-fitting existing vehicles.